Training this skill improves your chances of causing a stun on an enemy when you hit with a melee attack. This skill is not reliable, but is incredibly nice…if trained above 90%. This is a skill you either master or don’t bother with. Monsters have too much innate stun resistance to be dazed by an amateur in this skill.

The ingame help reads:

Skill duration: random.
Type of skill : neutral skill.
Affecting stats: Str/Dex.
It uses no endurance points.
One of the most powerful facets of hand to hand combat,
is the ability to land a blow that knocks your opponent 
senseless. A stunned opponent is unable to conduct his own
attacks, defend himself, or flee, which puts him at your
complete mercy. Those who are trained in the ability to
execute these blows, are able to do it more often and for
longer then those who are not.